Epidemiologic studies have demonstrated a close correlation between animal protein and total fat and the incidence of breast cancer. Experimental studies have focused on fat as the causative factor. However, recent studies from our laboratory and others have shown that increased dietary protein increased the incidence and aggressiveness of the DMBA-induced breast tumors. Limited animal studies by Clinton and Viseck has demonstrated a dietary protein-fat interaction related to an increased tumor incidence. Therefore, this research study is designed to determine whether high protein diets have a synergistic effect on high fat diets and also whether increased dietary protein (per se) enhance N-nitroso-N-methyurea (NMU) induced mammary tumor response. This study will utilize the carcinogen NMU because it is a direct carcinogen with a very short half-life and the induced mammary tumor is estrogen dependent and stimulated by growth hormone and prolactin. The experiments will also determine whether the high protein-high fat diets are exerting their influence during the initiating or promotional phase of the tumor development. The animals in all of these experiments will be fed the high protein-high fat diet throughout the period of brain development (gestation and lactation). This model will be compared to the usual protocol of initiating feeding schedules after weaning. Dietary protein and fat may influence tumor development through a neurohormonal mechanism. All diet protocols will be evaluated to determine its effect on serum estrogen, prolactin and growth hormone. At appropriate times hypothalamic biogenic amine concentration and turnover rates will be determined and pituitary growth hormone and prolactin also determined. These data will be evaluated to determine whether dietary excesses influence mammary tumorigenesis through a neurohormone mechanism. The studies will also evaluate the effect of the carcinogen, NMU, on neurohormonal regulation. Accordingly, hormone determinations will be made throughout the estrous cycle following NMU administration.